some aspect': it does not mean ignoring the other aspects, it is just doing justice to the fact that from this aspect's point of view, the other is irrelevant. It is being one- and multiple-track minded simultaneously." - Edsger W. Dijkstra
open if it is still available for extension. For example, it should be possible to add fields to the data structures it contains, or new elements to the set of functions it performs." CLOSED "A module will be said to be closed if [it] is available for use by other modules. This assumes that the module has been given a well-defined, stable description (the interface in the sense of information hiding)" - Bertrand Meyer